of this COST action. COST (an acronym translated from the French for European Cooperation in the Field of Scientific and Technical Research) is a European framework for the coordination of nationally funded research within Europe. A "COST action" operates within a bottom-up structure that is administered by individual scientists through working groups and a so-called management committee. This particular workshop was held in Zurich, Switzerland, on 24– 25 May 2001 and consisted of a series of scientific pre-sentations and an extensive discussion by all the par-ticipants (about 50 people from 18 countries). Extended abstracts of the individual presentations will be published as a proceedings volume by the Euro-pean Commission. They can be downloaded from the Web site of Working Group 1 (www.iac.ethz.ch/en/ research/cost715/cost715_2.html). In this contribu-tion a short outline of each presentation is given and the discussion is summarized. OVERVIEW OF THE PRESENTATIONS. S. E. Belcher (University of Reading) presented a new model for the flow in the lowest part of the urban boundary layer, that is, the roughness sublayer. The approach does not resolve individual buildings but rather treats the spatially averaged flow field with all its consequences. Scaling considerations were pre-sented as well as an approach for the turbulence clo-sure (mixing length approach). The model was shown to favorably correspond to available datasets (mainly from regular array wind tunnel or "semi-full-scale" physical modeling). An overview of various modeling approaches for urban applications in numerical models was given by R. Bornstein (San Jose State University). In broad terms, three types of approaches can be distinguished.